During a manufacturing process for manufacturing, for instance, semiconductor devices, a specific film formed on a processing target substrate such as a semiconductor wafer (hereafter may be simply referred to as a “wafer”) is selectively etched and removed by using a resist film formed at the surface of the wafer as a mask and then the resist film is removed through ashing. During the ashing process, oxygen radicals generated by exciting an oxygen-containing gas to a plasma state are used in the related art. As semiconductor elements today need to assume a multilayer structure with a greater number of wiring layers stacked one on top of another, a low dielectric constant film with a low dielectric constant, such as a low-k film, is frequently used as an insulating film in the multilayer wiring structure. Since such a low dielectric constant insulating film is readily damaged by oxygen radicals, hydrogen radicals with which damage can be more successfully inhibited are utilized when etching or ashing the low dielectric constant insulating film.
The plasma processing apparatuses that process wafers with radicals in the related art include those adopting a structure equipped with a plasma generation chamber where plasma is generated by exciting a processing gas and a processing chamber communicating with the plasma generation chamber (see, for instance, patent reference literatures 1 and 2 listed below). Since ions that are sure to damage films on a wafer are formed, in addition to radicals, from the plasma generated in the plasma generation chamber, a barrier wall member via which ions traveling from the plasma generation chamber toward the processing chamber are trapped but radicals are allowed to pass through is disposed between the plasma generation chamber and the processing chamber, in order to process the wafer with the radicals while minimizing damage to the wafer.
The barrier wall member in the related art is constituted with a single barrier wall plate with through holes formed therein, which is disposed with a horizontal orientation. However, at the barrier wall member constituted with a single barrier wall plate, the through holes formed to let through the radicals are unblocked, giving rise to a concern that ultraviolet light (including vacuum ultraviolet light) generated as the processing gas is raised to plasma in the plasma generation chamber may be transmitted through the through holes. If the ultraviolet light is transmitted through the through holes and is directly radiated over the surface of the wafer, films deposited upon the wafer may become damaged and accordingly, the wafer needs to be shielded from the ultraviolet light. For instance, if a low-k film is formed on the wafer, the Si—C bond in the low-k film is broken by the ultraviolet light, allowing carbon to separate, which will result in an increase in the dielectric constant of the film. In addition, the low-k film will be rendered more hydrophilic and the water content in the film will increase to result in a decrease in the mechanical strength of the film.
These issues may be addressed as disclosed in patent reference literature 1 listed below by constituting the barrier wall member with two barrier wall plates disposed with a horizontal orientation, which are stacked one on top of the other with a clearance formed between them and by setting the through holes formed at the individual barrier wall plates with an offset, so as to disallow transmission of ultraviolet light.
There is an issue yet to be addressed with regard to a barrier wall member constituted with a barrier wall plate disposed with a horizontal orientation as described earlier, in that since radicals collide with the surface of the barrier wall plate substantially at a right angle to the surface and thus tend to become lost after the collision, they cannot pass through the barrier wall plate with a high level of efficiency. Since such a reduction in the quantity of radicals passing through the barrier wall plate is bound to result in a decrease in the quantity of radicals that actually reach the wafer, the processing rate at which the wafer is processed with the radicals, e.g., the etching rate, the ashing rate or the film formation rate, will be lowered.
While the quantity of radicals passing through a barrier wall member constituted with a single barrier wall plate may be increased by forming a greater number of through holes or by forming larger through holes, ultraviolet light will be transmitted readily through such through holes. In addition, while the passage of ultraviolet light can be prevented more effectively with a barrier wall member constituted with a plurality of barrier wall plates, a significant quantity of radicals is likely to be lost through collisions, as, for instance, radicals having passed through the through holes at a barrier wall plate collide with the surface of another barrier wall plate located under the first barrier wall plate.
There is another concern in that the ease with which the gas flows as it passes through a barrier wall plate disposed with a horizontal orientation and having through holes formed therein, i.e., the conduction of gas, cannot be readily adjusted. For instance, as the processing gas flows at a higher flow rate, the flow velocity over a central area of the barrier wall plate will become higher than the flow velocity at the periphery of the barrier wall plate and the overall flow velocity distribution will assume a substantially parabolic curve. Under such circumstances, the radicals having reached the wafer will be distributed in different quantities at the central area and the peripheral area, which is bound to compromise the in-plane uniformity of the wafer processing. For these reasons, it is desirable to adjust the flow velocity of the gas passing through the barrier wall plate by adjusting the conduction at the barrier wall plate.
The conduction at the barrier wall plate may be adjusted by altering the quantity or size of the through holes. However, it is not easy to determine the optimal quantity or size of through holes for achieving the desired gas flow velocity distribution and thus, the conduction cannot easily be fine-adjusted. In addition, such a change in the quantity or size of through holes will necessitate replacement of the barrier wall plate itself. In short, conduction adjustment generally requires a great deal of attention and labor.    (patent reference literature 1) Japanese Laid Open Patent Publication No. 2006-073722    (patent reference literature 2) Japanese Laid Open Patent Publication No. 2002-083803